linux-kernel - Re: [PATCH] tsc: make calibration refinement more robust

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Date:   Fri, 2 Nov 2018 07:40:10 +0100
From:   Daniel Vacek <neelx@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     x86@...nel.org, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] tsc: make calibration refinement more robust

Hi Thomas,

thanks for checking.

On Thu, Nov 1, 2018 at 4:34 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> Daniel,
>
> On Thu, 1 Nov 2018, Daniel Vacek wrote:
>
> Please use 'x86/tsc:' as prefix. git log path/to/file usually gives you a
> reasonable hint about prefixes.

Oh, sure thing. The dmesg always prints 'tsc:' - I somehow sticked to it...

>> -#define MAX_RETRIES     5
>> -#define SMI_TRESHOLD    50000
>> +#define MAX_RETRIES  5
>> +#define TSC_THRESHOLD        (tsc_khz >> 5)
>
> This breaks pit_hpet_ptimer_calibrate_cpu() because at that point tsc_hkz is 0.

That did not show up with my testing, sorry. I guess
pit_calibrate_tsc() never failed for me. Hmm, actually it looks like
quick_pit_calibrate() does the job for me so
pit_hpet_ptimer_calibrate_cpu() is likely not even called. Would this:

#define TSC_THRESHOLD   (tsc_khz? tsc_khz >> 5: 0x20000)

work for you instead? Or alternatively at some point when chasing this
down I used:

#define TSC_THRESHOLD (0x10000 + (tsc_khz >> 6))

The first one seems better though. I can send v2 next week if you like it.

--nX

> Thanks,
>
>         tglx